Further progress continues to provoke an interest in the hypothesis that human growth hormone is a family of proteins. The hypothesis further makes an analogy between proinsulin activation by peptide deletion to two chain insulin (activated) by proposing that single chain 191 amino acid hGH (prohormone) is converted to activated, hormonal, hGH by deletions of amino acids in the 135 to 147 area, and that this substance (or set of substances) two chain hGH is the circulating form. The present research centers on devising specific radioimmunoassays and receptor assays for each form of pituitary hGH for measurements of their concentrations in pituitary glands and in blood in growth problems and in breast cancer, as well on testing metabolic activities in short term studies of monomeric single chain hGH compared to two chain hGH.